Dutar P, Vu H M, Perkel D J
Department of Neuroscience, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6074, USA.
J Neurophysiol. 1998 Oct;80(4):1828-38. doi: 10.1152/jn.1998.80.4.1828.
Nucleus HVc of the songbird is a distinct forebrain region that is essential for song production and shows selective responses to complex auditory stimuli. Two neuronal populations within HVc give rise to its efferent projections. One projection, to the robust nucleus of the archistriatum (RA), serves as the primary motor pathway for song production, and can also carry auditory information to RA. The other projection of HVc begins a pathway through the anterior forebrain, (area X --> medial portion of the dorsolateral nucleus of the thalamus (DLM) --> lateral portion of the magnocellular nucleus of the anterior neostriatum (L-MAN) --> RA) that is crucial for song learning but, although active during singing, is not essential for adult song production. To test whether these different projection neuron classes have different functional properties, we recorded intracellularly from neurons in nucleus HVc in brain slices. We observed at least three classes of neuron based on intrinsic physiological and pharmacological properties as well as on synaptic inputs. We also examined the morphological properties of the cells by filling recorded neurons with neurobiotin. The different physiological cell types correspond to separate populations based on their soma size, dendritic extent, and axonal projection. Thus HVc neurons projecting to area X have large somata, show little spike-frequency adaptation, a hyperpolarizing response to the metabotropic glutamate receptor (mGluR) agonist (1S,3R)-trans-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), and exhibit a slow inhibitory postsynaptic potential (IPSP) following tetanic stimulation. Those HVc neurons projecting to motor nucleus RA have smaller somata, show strong accommodation, are not consistently hyperpolarized by ACPD, and exhibit no slow IPSP. A third, rarely recorded class of neurons fire in a sustained fashion at very high-frequency and may be interneurons. Thus the neuronal classes within HVc have different functional properties, which may be important for carrying specific information to their postsynaptic targets.
鸣禽的HVC核是一个独特的前脑区域，对鸣叫产生至关重要，并且对复杂听觉刺激表现出选择性反应。HVC内的两种神经元群体产生其传出投射。一种投射到古纹状体粗核（RA），作为鸣叫产生的主要运动通路，也可以将听觉信息传递到RA。HVC的另一种投射开始了一条通过前脑的通路（X区→丘脑背外侧核内侧部分（DLM）→新纹状体前部大细胞外侧核（L-MAN）→RA），这对鸣叫学习至关重要，但尽管在鸣叫时活跃，对成年鸣禽的鸣叫产生并非必不可少。为了测试这些不同的投射神经元类别是否具有不同的功能特性，我们在脑片中对HVC核中的神经元进行了细胞内记录。基于内在生理和药理特性以及突触输入，我们观察到至少三类神经元。我们还通过用神经生物素填充记录的神经元来检查细胞的形态学特性。不同的生理细胞类型根据其胞体大小、树突范围和轴突投射对应于不同的群体。因此，投射到X区的HVC神经元具有大的胞体，几乎没有放电频率适应性，对代谢型谷氨酸受体（mGluR）激动剂（1S，3R）-反式-1-氨基环戊烷-1，3-二羧酸（ACPD）有超极化反应，并且在强直刺激后表现出缓慢的抑制性突触后电位（IPSP）。那些投射到运动核RA的HVC神经元具有较小的胞体，表现出强烈的适应性，不会被ACPD持续超极化，并且不表现出缓慢的IPSP。第三类很少被记录的神经元以非常高的频率持续放电，可能是中间神经元。因此，HVC内的神经元类别具有不同的功能特性，这对于将特定信息传递到其突触后靶点可能很重要。
